For the output of safety-relevant signals to actuators, such as, for example, contactors, motors, relays, etc., for switching, i.e., for activating or deactivating a load circuit for performing a certain safety-related application, in particular, in safety engineering, strict requirements are placed on error recognition and failure behavior of the circuit, as well as the peripherals, which must also satisfy, for example, DIN EN 954-1 or IEC 61508 standards. For satisfying these requirements, typically two-channel structures are used for controlling the load circuit.
These two-channel structures are based on the fact that two or more actuators are integrated into the load circuit for generating safety-relevant redundancy and are controlled specific to the application. For monitoring proper switching, as a rule, there are readback circuits connected to the actuators. For testing and monitoring such two-channel structures, for certain states of the actuators, corresponding readback signals are detected and evaluated by means of a readback circuit.
For performing certain tests, if control signals must be output to the actuators, they are frequently visible on the output and can consequently interfere with a connected load. This also applies, for example, when the test phase is kept rather short, because, for example, even for fast-running machines connected via the load circuit, in which, for example, a linear motor is used, only a few milliseconds are required for them to reach their final velocity. Consequently, in such cases, conventionally only one test or one monitoring sequence is performed before the actual use of the circuit structures and not during the use for safety-related application specific to the application.